How to Make It
Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; pound to 1/3-inch thickness using a meat mallet or small heavy skillet. Sprinkle chicken evenly with salt and 1/4 teaspoon pepper and drizzle with 1/2 teaspoon olive oil. Heat a large nonstick skillet over medium-high heat. Add chicken to pan; cook 5 to 6 minutes on each side or until browned.
While chicken cooks, cut shallots vertically into thin slices. Remove chicken from pan. Coat pan with 1/2 teaspoon olive oil. Add mushrooms and shallots to pan. Cook 1 minute, stirring constantly. Stir in sherry and marjoram. Return chicken to pan; cover and cook 3 to 4 minutes or until mushrooms are tender and chicken is done. Transfer chicken to a platter. Pour mushroom mixture over chicken; sprinkle with freshly ground pepper, if desired. Serve immediately.